The present invention relates generally to the field of removal of polymeric materials from a substrate. In particular, the present invention relates to compositions and methods as pre-treatments for the removal of polymer material, and particularly plasma induced polymeric material, from electronic devices.
Numerous materials containing polymers are used in the manufacture of electronic devices, such as circuits, disk drives, storage media devices and the like. Such polymeric materials are found in photoresists, solder masks, antireflective coatings, and the like. For example, modern technology utilizes positive-type resist materials for lithographically delineating patterns onto a substrate so that the patterns can be subsequently etched or otherwise defined into the substrate material. The resist material is deposited as a film and the desired pattern is defined by exposing the resist film to energetic radiation. Thereafter the exposed regions are subject to a dissolution by a suitable developer liquid. After the pattern has been thus defined in the substrate the resist material must be completely removed from the substrate to avoid adversely affecting or hindering subsequent operations or processing steps.
It is necessary in such a photolithographic process that the photoresist material, following pattern delineation, be evenly and completely removed from all unexposed areas so as to permit further lithographic operations. Even the partial remains of a resist in an area to be further patterned is undesirable. Also, undesired residue between patterned features can have deleterious effects on subsequent film depositions processes, such as metallization, or cause undesirable surface states and charges leading to reduced device performance.
Numerous polymer stripper compositions have been developed to remove positive and negative photoresists. For example, U.S. Pat. No. 5,962,197 (Chen) discloses a composition for removing photoresists or soldermasks containing 30-80% by weight of a propylene glycol ether, 10-60% by weight of a pyrrolidone, 0.1-5% by weight of potassium hydroxide, 0.1-10% by weight of a surfactant, 0-20% by weight of 1,3-butanediol, 0-10% by weight of 2-(2-) aminoethoxy)ethanol and a water content of &lt;1%. Other compositions are known that contain amines, such as alkanolamines, or tetraalkylammonium hydroxides, such as tetramethylammonium hydroxide, as the active polymer removing agent. Surfactants may optionally be used in such compositions. See, for example, PCT patent application WO 88/05813 (Martin et al.) which discloses a mixture having a selected solvent as the major component and a tetraalkylammonium hydroxide as a minor component and optionally a surfactant.
The semiconductor industry is moving toward sub-quarter micron geometry features. As the geometry of the features gets smaller and pattern density increases, plasma etching, reactive ion etching, ion milling and the like are required for the lithographic process. During such plasma etching, reactive ion etching and ion milling processes, the polymeric material is subjected to conditions that make the removal of such polymeric material difficult. During the plasma etch process a photoresist film forms a hard to remove organometallic polymeric residue on the sidewalls of the various features being etched. Furthermore, the photoresist is extensively cross-linked due to the high vacuum and high temperature conditions in the etch chamber. Known cleaning processes do not acceptably remove such polymeric residue. For example, acetone or N-methylpyrrolidinone is currently used at extreme conditions, which include high temperature and extended cycle times. Such use conditions are often above the flashpoint of the solvent which raises certain environmental, health and safety issues regarding operator exposure. In addition, productivity and throughput are adversely affected by the extended process cycle times required. Even with such extreme stripping conditions, the devices may have to undergo wet strip followed by de-scum (O.sub.2 plasma ash) and a subsequent wet clean for a wet-dry-wet strip process.
Known stripping compositions for post-plasma etch polymer removal applications have numerous drawbacks including, undesirable flammability, toxicity, volatility, odor, necessity for use at elevated temperatures such as up to 100.degree. C., and high cost due to handling regulated materials. A particular problem with advanced next generation semiconductor devices is that known stripping compositions are incompatible with a variety of thin films in such devices, that is, such known stripping compositions cause corrosion of the thin films, specifically copper, and low-k dielectric material present in such advanced devices.
Methods for increasing the effectiveness of polymer removers have been proposed. For example, U.S. Pat. No. 4,786,578 (Neisius et al.) discloses a rinse solution used after a photoresist stripper. This rinse solution contains a nonionic surfactant and an organic base, such as an alkanolamine, that will form a water-soluble salt with alkylbenzenesulfonic acids. U.S. Pat. No. 4,824,762 (Kobayashi et al.) discloses a photoresist stripper post rinse containing a glycol ether and an aliphatic amine. In both patents, the compositions contain amines which tend to cause corrosion of copper present in the electronic devices. A pretreatment has been proposed using hot (110-125.degree. C.) solvent, see U.S. Pat. No. 4,202,703 (Zuber et al.). In this patent, the pretreatment was followed by a stripper containing a tetraalkylammonium hydroxide and then a post rinse with 1,1,1-trichloroethane. Such a process raises a number of environmental concerns.
There is thus a continuing need to effectively remove polymeric material, including post plasma etch polymeric material, from electronic devices in ways that are environmentally compatible, that do not damage the features and geometries of the electronic devices, that do not cause corrosion of the substrate, particularly thin metal films, and that do not etch dielectric layers in the substrate.